Controlled release pesticidal compositions offer several possible advantages over conventional compositions. First, they are more economical, as fewer pesticide applications to the crop are necessary. Controlled release compositions offer safety to the environment by preventing pesticide overuse and run-off or soil (translocation) leaching into unwanted neighboring areas such as water ways. They also offer safety to the crop in instances when large doses of conventional formulations are phytotoxic and offer safety to workers applying pesticides in the field by reducing human toxicity. Finally, controlled release compositions allow the effective use of pesticides which are too rapidly degraded or volatilized in conventional formultions (i.e., conventional pesticides with very low residual activity).
Many types of controlled release pesticidal compositions, however, suffer from disadvantages as well. One type, microcapsules, consist of an external polymeric barrier and an internal active core. Although microcapsules can provide effective controlled release, they are expensive to produce as solvents are necessary, there are process difficulties in isolating intact, non-leaking capsules, and recycle is difficult. In addition, the microcapsules can be difficult to formulate. It is difficult to produce capsules small enough for a wettable powder formulation. Even when small capsules are made, they are often inefficient as they tend to roll off plant surfaces due to their spherical shape. In addition, microcapsules cannot easily be made into granular formulations.
Another known type of controlled release pesticidal composition, overcoated carriers, consists of a porous, inert, solid core (e.g. clay particles or a porous plastic) into which the active ingredient is absorbed, the core then being overcoated with a barrier layer (polymers or waxes). These compositions suffer the same general disadvantages as microcapsules. They are expensive to produce because solvent processes are necessary, and careful overcoating is needed to produce a product with reproducible release rates. They can also be difficult to formulate. For example, overcoated carriers are usually unsuitable as wettable powders because particles agglomerate during the overcoating step and are too large for such a formulation.
The one-phase controlled release pesticidal compositions described in the art also suffer certain advantages. Many are prepared via expensive solvent processes. Nearly all are not very friable and are thus unsuitable for milling to a fine wettable powder. Many such compositions undergo phase separation during processing (e.g. grinding to particles) and thus lose much of their ability to control the release of the pesticide.
Very few of the known one-phase compositions provide for a homogeneous matrix-active ingredient combination. In one type of homogeneous composition, the active ingredient is chemically bound to the matrix, the matrix generally being a polymer with pendant, reactive functional groups. These compositions are expensive to produce and are also expensive to market as the compositions must often be registered as new compounds and extensively tested before use. Furthermore, the choice of pesticides is very limited, since only those with reactive functional groups may be used.
Other known one-phase, homogeneous compositions do not involve chemically-bound active ingredients but utilize barriers which do not provide effective controlled release for most pesticides. Many of these compositions will also undergo phase separation upon storage or will cake when in particulate form.
There thus exists a clear need for controlled release pesticidal compositions which avoid the problems inherent in the prior art compositions.